Alternative Definitions of SDN

Chapter 6 commences with an inventory of the drawbacks most commonly cited about Open SDN. For each, we attempt to assess whether there are reasonable means to address these drawbacks. In some cases, some of the disadvantages of Open SDN have been addressed by proposed alternative SDN solutions that do not exhibit these flaws. In Chapter 6 we provide details of the two alternative SDN approaches we introduced in Chapter 4, SDN via Existing APIs and SDN via Hypervisor-Based Overlays. We go deeper in our examination of SDN via Existing APIs, as this particular category of SDN has increased in importance in the past few years, pulling in protocols such as NETCONF and the new BGP-LS/PCE-P plug-in for OpenDayliglht. In addition, we introduce a third alternative, SDN via Opening up the Device. We discuss another class of networking solutions, known collectively as Network Functions Virtualization (NFV). NFV is frequently associated with SDN, but it is distinct and should not be considered as yet another SDN alternative. There is overlap, though, between SDN and NFV, which we explain in this chapter. We offer a reasonably objective means of evaluating to what degree each of these alternatives is a true SDN solution. Some of the criteria that we use are the five fundamental traits of Open SDN that we defined in earlier chapters. To make this ranking mechanism fairer, we include whether each alternative suffers the same drawbacks as those of Open SDN. Admittedly, this remains a bit subjective, as our litmus test is not absolute. The ranking is made somewhat more difficult because of a lack of agreement in the industry about the exact definitions of the alternate categories and by the fact that in some cases, the different alternatives overlap. Without providing any absolute judgment about winners or losers, our hope is that this SDN report card will help others make decisions about which, if any, SDN technology is appropriate for their needs.